Exponential and Logarithmic Functions · Superchallenge problem

On the Richter scale $M=\log\dfrac{I}{I_{0}}$, earthquake C has magnitude $4.2$. Earthquake B is $5$ times as intense as C, and earthquake A is $100$ times as intense as B. Find the magnitudes of A and B (two decimals).

Round your answer to the nearest hundredth.